This invention relates generally to engine mounts that are used to mount an automotive vehicle engine to the automotive vehicle chassis. More specifically, the invention relates to engine mounts that have improved vibration isolation but do not allow excessive engine displacement. The mounts are particularly useful in medium and heavy duty trucks.
In automotive vehicles such as trucks, it is customary practice to mount the engine on the chassis by means of engine mounts. Such mounts typically comprise a combination of metal and elastomeric parts. In order to be acceptable, an engine mounting system must meet several requirements. In particular, the engine mounts must be strong and durable, and they must provide a satisfactory level of vibration isolation without allowing excessive engine motion.
Heretofore, most engine mounting systems for medium and heavy duty trucks were designed to have isolators with fairly high stiffnesses in order to maintain adequate fatigue life and to limit engine motion to an acceptable level. Unfortunately, mounts of this design provided less than optimum vibration isolation performance.
The present invention relates to new and improved engine mounts which provide adequate fatigue life and good vibration isolation performance while limiting engine motion to an acceptable level. A mount according to principles of the present invention is constructed of a new and unique organization and arrangement of metal and elastomeric parts so as to have a relatively low stiffness vibration isolator portion, about the nominal static design loads, in combination with snubber portions that limit excessive engine displacement. Specific examples of mounts will hereinafter be disclosed as preferred embodiments of the invention.
Specific geometries of the metal and elastomeric parts comprising each mount can provide different stiffnesses along the principal axes of each mount to obtain desired vibration isolation levels and hence limit vibration inputs into the truck. When higher input loads are applied to the mounts, the snubbers become active to limit displacement between the engine and chassis at each location along any mount axis where there is a relatively high input load component. Since relatively high input loads to the mounts are normally relatively infrequent during normal driving, the result will be reduced vibration and noise levels, and consequently a more comfortable and less fatiguing ride for the driver during normal driving.
In the preferred embodiment of mounts that will be hereinafter described, the vibration isolator portion comprises a discrete volume of elastomeric material (i.e. rubber) in the mounts having been cored out and metal parts of the mounts having been made in various rectangular and circular shapes. These features contribute to the ability to obtain different mount stiffnesses along each of the three principal axes of the mount, and in turn obtain an engine mounting system with desired stiffnesses in the three directions at each mount whereby the desired natural frequencies of the engine on the mounts are obtained. To ensure that engine motion is not excessive, built-in snubbing is provided at each mount. This snubbing prevents excessive engine motion that might otherwise occur when large torque and/or road load inputs are applied to the mounting system. Furthermore, the mounts are constructed and arranged to keep the engine captured in the chassis under extreme loading conditions.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings illustrate preferred embodiments of front and rear engine mounts according to the best mode contemplated at the present time in carrying out the invention.